The invention relates to vascular repair devices and, in particular, to an approach for designing intravascular stents in which the flexibility profile, the drug coating and/or the radiopacity are modified to meet specific design goals.
Stents are generally tubular-shaped devices which function to hold open a segment of a blood vessel. They also are suitable for use to support and hold back a dissected arterial lining that can occlude the fluid passageway. That is, whether self-expanding or expandable using force, stents are delivered within vasculature in a radially compressed configuration and then implanted at an interventional site while assuming a radially expanded configuration. At present, there are numerous commercial stents being marketed throughout the world. For example, some known prior art stents have multiple cylindrical rings connected by one or more links. While some of these stents are flexible and have the appropriate radial rigidity needed to hold open a blood vessel, there typically is a tradeoff between flexibility and radial strength and the ability to be tightly compressed or crimped onto a catheter so that it does not move relatively to the catheter or dislodge prematurely prior to controlled implantation at an interventional site.
Various conventional stents can include a plurality of rings connected by links. In certain stents, the rings include a plurality of peaks and valleys connected by bar arms. When these rings are positioned in phase relatively to one another, W-crests and Y-crests are formed at the points of connection between the links and rings. Once a stent embodying this structure is implanted at an interventional site, a significant amount of strain is placed upon the peaks and valleys. In fact, the link can become angulated or twisted upon stent expansion resulting in an overall twisted stent configuration. Such a twisted stent configuration can suffer from inadequate vessel wall apposition and thus, may not perform optimally in holding a vessel open. Further, the degree of twisting often cannot be predicted due to manufacturing and material variability which consequently limits the reliability of stent function.
Other factors also contribute to the unpredictability of stent performance. That is, conventional stents embody a pattern of links and rings which can be characterized as directional in configuration. A typical stent can include a pattern of adjacently arranged rings which extend the length of a stent and includes a first end which differs from that of a second end of the stent. Due to this directional structure, such a stent must be placed upon a catheter in a particular direction so that when it is deployed and implanted within vasculature, the stent will be arranged as contemplated to achieve expected performance. Unfortunately, conventional stents embodying directional structure can be placed on a catheter incorrectly due to operator error, and it is difficult to either identify this error or to correct it during a surgical procedure.
Conventional stents can also be typically designed to have a relatively uniform flexibility across the length of the stent. However, this uniform flexibility is often not optimal for moving the stent through curved portions of the body. Accordingly, what has been needed and heretofore unavailable is a stent that is particularly more flexible at one or both ends than the center portion of the stent for better movement through the body.
Additionally, conventional stents tend to have a uniform drug coating. This can be problematic when, for example, the physician overlaps stents. Accordingly, what has been needed and heretofore unavailable is a stent that has greater drug coating on the center portion of the stent as compared to one or both ends of the stent. It can be particularly desirable to combine this non-uniform drug coating with a stent having superior flexibility at one or both ends, as described above.
Further, conventional stents tend to be uniformly radiopaque. However, this uniformity can present problems when, for example, a physician overlaps stents and needs to better monitor the overlapped regions of the stent. Consequently, what has been needed and heretofore unavailable is a stent that has enhanced radiopaque properties at one or both ends of the stent, as compared to the center portion of the stent.
Accordingly, what is needed is a stent including structure which provides desired flexibility without compromising radial strength and reduces unwanted stresses and twisting. Also, there is a need for a stent which addresses problems associated with directional stents. Moreover, there is a need for a stent which addresses problems associated with stent on satisfies these and other needs. The present invention satisfies these and other needs.